This invention relates to a method of making a photoconductive layer, and especially to a method of making a photoconductive layer having a high photosensitivity and a high uniformity.
There are known in the art several methods for making the photoconductive layer, such as the sintering method, evaporation method and dispersion method. However, these conventional methods are not satisfactory for providing a photoconductive layer which can be used for a practical device such as an image converting panel for converting a pattern of radiations into a visible image.
For example, in order to provide a photoconductive layer of a considerable size and thickness, there is suitably used the conventional dispersion method, in which the photoconductive material in powdered form is uniformly dispersed in a binder and a suitable solvent is added thereto. Then, the mixture is applied by the screen method or squeezing method, and after that it is dried and hardened. In this case, in order to make the powder of the activated photoconductive material photosensitive, it is necessary that the powder have considerable grain size, such as one to several microns or higher than 10 microns in many cases. Further, as the photosensitivity is decreased according to increase of the amount of the binder, the amount of the binder is limited. Moreover, since the photosensitivity is apt to decrease by mixing to the extent needed for dispersing the powder uniformly, it is not mixed enough. Therefore, when using such conventional solution, there are several disadvantages such as non-uniformity and poor reproducibility of the resultant layer. Thus for the device using such photoconductive layer, this causes poor picture quality, resolution and photosensitivity, and poor reproducibility of the characteristics and low yield of the device, especially for the device using a layer size panel.